In the age of bits and bytes, where more and more messages, information and other digital data are being transmitted by cable and air, there is also an increasing demand from owners of digital data to protect said data.
Protection against unauthorized access to the data is a significant feature, because only people who pay for access to the data, for example, are also intended to enjoy these data. One example of this is pay TV (e.g. the television channel “Premiere”).
As already indicated above, there are two kinds of requirements for protection:                protection of content, i.e. a file is intended to be able to be accessed only by the user who has actually paid for it. This is also called content protection.        Protection of services, i.e. data provided as part of a service, for example a live-broadcast football match, are intended to be able to be received only by those who actually have the access rights for this. This is also called service protection. Service protection is particularly suitable for a service with a continuous data stream (streaming), such as TV, radio etc.        
Whereas the protection of individual files (content protection) normally involves the generation of a rights object which ties the file to be protected to itself, the protection of services often involves the transmission of chronologically successive cryptographic keys with a limited validity time which allows the data stream/service to be decrypted.
It may now occur that the subscriber using a service is allocated a traffic encryption key with a life for a service from the service provider which is valid far beyond the end of the content (e.g. a feature film). This condition is undesirable to the service provider, since the subscriber would be able to access content for which he has not paid.